Tunable interface properties of correlated and topological materials

Louisiana State University, Baton Rouge LA

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research, and education focused on the discovery and manipulation of materials properties and phenomena at surfaces and interfaces of recently discovered and predicted classes of insulators and superconductors, and hybrid materials and structures involving these or these in combination with strongly correlated materials. Topological insulators are insulating materials that do not conduct electricity in the bulk but are surrounded by metallic states that cover the surfaces, edges, and interfaces. Similarly topological superconductors are thought to be like ordinary superconductors in the bulk in that they conduct electricity without loss, but their surfaces and edge are enveloped in a fundamentally new quantum state of electrons with unusual properties. Hybrid structures of these materials and ones that include strongly correlated materials, that is materials where the strong interactions among electrons lead to unusual properties that arise from the correlated motion of electrons, are promising ingredients to discover new phenomena which are interesting in their own right and may form the basis of new electronic device technologies for a wide range of applications. The PI aims to build on previous work and investigate how the properties of a topological material in the boundary region at and near the surface of a topological material influence the properties of the surface states that envelope the topological material. Some properties of strongly correlated materials are more tunable than their analogs in more conventional materials, making them interesting candidates for technological applications. However, complete understanding and control of these functionalities is an ongoing challenge. This is especially true at interfaces that form the backbone of realistic devices, in large part because the behavior of a material near a surface may differ qualitatively from that in the bulk. This award supports research that builds on the PI's previous work to connect the magnetic properties near the surfaces of topological superconductors and insulators with realistic descriptions of both bulk and surface physics. The PI will investigate hybrid devices combining superconductors, magnets, and topological electronic materials, and establish new strategies to control their properties and discover new phenomena. This award supports the discovery new materials and materials-related phenomena that contribute to the knowledgebase for future information technologies, and energy and related applications. Research will be performed in collaboration with groups both in the US and in Europe. Developing techniques that combine theoretical and computational approaches pursued under this award will help train a new and diverse generation of students, and prepare them for a variety of careers in academia and in industry. TECHNICAL SUMMARY This award supports theoretical and computational research, and education that is focused on surface properties of topological materials, and their interfaces with strongly correlated electron materials. A key aspect of the research is to develop a realistic description of the boundary at surfaces and interfaces and understand how the boundary affects the surface states of topological matter. Previous work shows that boundaries play an essential qualitative role in determining the magnetic properties of topological insulator surface states. Moreover, subdominant order parameter in topological superconductors can give rise to static magnetism. Building on these results, the PI will develop methods to address in detail the magnetic, spin transport, and superconducting properties of hybrid structures of topological matter with magnetic, superconducting, and other correlated electron systems. Among the crucial ingredients of the models are the absence of inversion symmetry at the interface, and its interplay with the strong spin-orbit interaction characteristic of the bulk. To make progress, the PI will combine theoretical methods of many-body physics with computational techniques. Since the magnetic properties of the surface state depend on the details of the bulk band structure, the PI will collaborate with colleagues performing first-principles calculations to make materials-specific predictions. Research performed under this award aims: to establish how to control the magnetic and spin transport properties of the topological surface states, and to achieve spin control over proximity and Josephson coupling and vice versa. These studies will advance understanding of correlated electronic matter both for applications and in search for novel quantum phenomena. Research will be performed in collaboration with groups both in the US and in Europe. Developing techniques that combine theoretical and computational approaches pursued under this award will help train a new and diverse generation of students, and prepare them for a variety of careers in academia and in industry.